M. Ussow’s Zoologico-Embryological Investigations. 209 
splendid addition to the elucidation of Australian natural his- 
tory; and it is to be hoped that another grant will be made 
by our liberal Legislature to enable the author to finish his 
great undertaking. 
XX VIL.—Zoologico-Embryological Investigations. 
By M. Ussow. 
{ Continued from p. 113. } 
IV. Appearance of the Organs. 
We may now pass to the second period *, that of the pro- 
duction of the organs. On the first day of this period (in 
Sepiola and Loligo the ninth day from the beginning of the 
process of segmentation) the rhomboidal groove already de- 
scribed gradually becomes deeper, and covered over by the 
elongate-ovate constantly growing fold, which is separating 
by constriction at the ventral side and assuming the form of 
a shield. ‘Towards the end of this period the margins of the 
fold begin to grow together, and the rhomboidal groove 
becomes converted into a flat tube, somewhat broader in the 
middle (especially in Sepia). 
The scutiform hill-like elevation (originating from the co- 
alesced fold) which lies over the tube chiefly on the dorsal 
surface, and which is gradually constricted, is the rudiment 
of the mantle; whilst the os Sepie will subsequently be 
formed in the above-mentioned tube closed at both ends and 
widest in the middle (Sepia, Loligo, Sepiola, Ommastrephes, 
Rossia). ‘The elevation, separating by constriction at the 
ventral side, grows both upwards and downwards, and ac- 
quires first the form of a cup and then that of a cylinder. 
The walls of the so-called primitive groove t, which is con- 
* In Loligo, Sepiola, and Argonauta the second period of development 
lasts five days. In this paper I follow Metschnikoff’s division of the 
development of the Cephalopoda into three consecutive periods :—first, 
the formation of the germ-lamelle; second, the appearance of the 
organs ; third, the gradual further development of the organs. 
+ The position of this rhomboidal depression upon the dorsal surface 
its early appearance (before all the organs), its further mode of develop- 
ment, are all facts which remind us of the primitive groove of the Verte- 
brata: and taking them into consideration, it may likewise be called the 
primitive groove, although as a matter of course there can be no question 
of comparing it more closely with the primitive groove of the Vertebrata, 
as the two rudiments represent fundamentally different organs. Although 
a groove is also at first formed in the Octopoda (Argonauta), this does 
not become closed (except in the genus Cirrhoteuthis?), but becomes era- 
dually effaced and finally disappears entirely. With regard to Argo- 
nauta, I must remark that Kolliker has described and figured the groove 
(l. e. p. 163, Taf. vi. figs. 71-73) as “a rather deep, funnel-shaped pit.” 
